"Glades don't burn..."
"Glades don't burn," said one of my undergraduate professors at Middle Tennessee State University in 2002, in response to my question about whether fire would be an appropriate management tool in the limestone glade ecosystem of central Tennessee's Nashville Basin.
Not being educated enough at that point in my career to articulate a response, I accepted the answer and then went about my way repeating the same mantra to others for the next several years. But then, in autumn 2008, my perspective changed.
Theo Witsell, botanist for the Arkansas Natural Heritage Commission and now also Director of Research for SGI, came to Nashville for the 2008 Natural Areas Conference. While in town, he visited the limestone glades southeast of Nashville during one of the conference field trips. I wasn't along on the same trip as he but afterward he asked, "what's going on with your glades?"
"What do you mean?" I asked.
He said, "there is an impenetrable thicket around each glade. In Arkansas, we are managing glade complexes with prescribed fire. There should be grassy savanna and open woodland around the edges of glades rather than an abrupt wall of redcedar and impenetrable shrub thickets."
My reply? "No way man. Glades don't burn. Fire is not important in these communities. Glades are edaphically maintained."
As you can see, I was repeating what I had been told a few years earlier. By this point, I was in a much better position to argue my point after having read extensively the papers of renowned cedar glade ecologists, Jerry and Carol Baskin (Univ. of KY), and their mentor, Dr. Elsie Quarterman (Vanderbilt Univ.), none of whom considered fire important in the ecology of limestone glades.
Theo explained that in Arkansas and Missouri, they manage glades of various types (shale, sandstone, igneous, dolomite, limestone) with fire. He acknowledged that while the glade proper may not burn due to high abundance of rock and paucity of fuels, that they routinely manage the surrounding habitats with fire, with much success.
He pulled out his computer and showed me a couple of PowerPoint presentations that showed dense thickets around glades that were thinned heavily leaving only a few scattered hardwoods (particularly post, blackjack and chinkapin oaks) and then burned. The before and after photos were dramatic and conservative grassland species rebounded quickly where previously there was very little herbaceous diversity. The resulting structure was a complex of glades embedded in open grassy savannas or very open woodlands, characterized by scattered twisted and gnarled old oaks, with a nearly continuous and rich graminoid/herb layer, punctuated throughout with scattered shrub thickets.
Meanwhile, I began to contemplate my own experiences in the limestone glades of central Tennessee. Much of the focus in limestone glades of central Tennessee (and for that matter in other limestone glades of the Southeast such as the Moulton Valley of north AL, the Ridge and Valley of e. TN, sw. VA, and nw. GA, and the Pennyroyal Plain of sc. KY) has always been on the open glades proper, characterized by high exposures of bedrock or broken gravel/flagstone. It was in these situations where the majority of the endemic glade species occur. Species such as Nashville Breadroot (Pediomelum subacaule), Gattinger's Prairie Clover (Dalea gattingeri), and Limestone Fameflower (Phemeranthus calcaricus) are just three of more than two dozen endemics. While these species are geographically restricted they are often not rare in the glades and may in fact be dominant. This is true of many of the other glade endemics.
But a second class of species often considered rare within the limestone glades are species that are often much more widespread geographically but their populations in the glades are either at the edge of the main range or they are disjunct-far removed-from the main set of populations of that species. Species such as White Four O'Clock (Mirabilis albida), Prairie Gentian (Gentiana puberulenta), Gattingeri's Goldenrod (Solidago gattingeri), Purple Prairie Clover (Dalea purpurea), Prairie Dropseed (Sporobolus heterolepis), and Wavy-leaved Purple Coneflower (Echinacea simulata) are each very rare in the limestone glades of central Tennessee. The main geographic distributions of these species is to northwest or west of central Tennessee, in the Midwestern tallgrass prairies or Ozark barrens and glades.
Unlike the endemic species that require the open shallow-soiled habitats, these species tend to occupy deeper-soils (but still shallow and rocky by comparison with richer soils in the region) of sloping limestone barrens or glade edges, sites dominated by perennial grasses and shrubs versus the annual grass dominated open glade habitats. For a definition of glades vs. barrens adopted by SGI see https://www.segrasslands.org/guide-to-the-grasslands-of-the-midsouth/.
It is this second class of species, not the majority of the limestone glade endemics, that are on the brink of disappearing entirely from the Basin. There are a few notable exceptions to this. The former federally-threatened Tennessee Coneflower (Echinacea tennesseensis), the federally-endangered Pyne's Groundplum (Astragalus bibullatus) and Limestone Clover (Trifolium calcaricum) are exceptions. They are all very narrow endemics and the clover and groundplum are each known from only a handful of populations and are both struggling to survive.
What is presumably the Limestone Clover was described by Augustine Gattinger in 1901 as "very common in the glades of middle Tennessee." Today, however, it is known from just three counties in Tennessee from five or fewer populations. Pyne's Groundplum is known today from a single county from about five populations.
Recent work by the Matthew Albrecht and Quinn Long of the Missouri Botanical Garden showed that Pyne's Groundplum, which often occurs near glade edges, benefits from manual removal of shrub and woody plant cover. Similar work needs to be done for the clover, for at least a couple of the populations I've observed are extremely suppressed with limited flowering and a high incidence of vegetative growth, presumably because they aren't getting enough light. In both species, reproduction seems very limited.
Albrecht and Long dug a little deeper into the history of the limestone glades of Rutherford County, Tennessee (literally the epicenter of limestone glades) to search for extra clues to explain their results. They examined witness tree records in the local archives from the late 1700s. What they found is that redcedar accounted for just 2 percent of the reported trees in those early land surveys. Oaks were most common, followed by "stakes." In those days, many of the land grants in the region were being awarded to Revolutionary War soldiers from North Carolina. Surveyors would mark off the boundaries of a given property and would note the tree species (witness trees) on the property boundary. When surveyors were delineating property boundaries, if they encountered open areas with no trees they would use a wooden "stake" to mark the boundary. In rocky areas, like the glades, they also frequently used "stacks" of rocks in similar fashion. Therefore, the relative abundance of stakes or stacks in early land surveys can be used to infer openness of the historical landscape.
Recently, a team of three historians from the Nashville area, published an incredible body of work. They spent decades studying and mapping tens of thousands of land survey records in the State Archives in Nashville for most of Middle Tennessee and published their work in four separate books and supplements. Check their website for more details (http://www.cumberlandpioneers.com/). Their work covers the period from 1789-1804 and spans properties from the Kentucky line in the north to the Alabama line in the south and includes all of the Nashville Basin. SGI is working to have these survey records entered into ArcGIS so we can see patterns of concentrations of stakes, etc. These records support the findings of Albrecht and Long and preliminary assessment of the relative abundance of stakes and stacks and oaks (particularly post oaks) indicates that major portions of the Nashville Basin were open at the time of first settlement of the region.
These open landscapes weren't restricted to areas around limestone glades. Surprisingly, the land survey data suggests other areas traditionally thought to be heavily forested were also open. For example, a large section of southwestern Rutherford County was recorded as open in these early land surveys and it remains one of the few areas in the state with Mollisol soils (Caitlin Elam, TN Division of Water Resources, pers. comm.), soils that are characteristic of Midwestern grasslands. Even some portions of the Outer Nashville Basin, areas with deep, phosphate-rich soils, may have been open or partially open. The upscale community of Belle Meade (=beautiful meadow) is one such Outer Basin opening. Numerous significant Paleoindian archaeological sites, Woodland Era Sites, and Mississippian Culture sites are located in these richer sections of the Outer Basin.
Open areas associated with glades were likely maintained by a combination of lightning fires in the region. The vegetation is often parched and drought stressed while those of stream valleys in deeper, richer soil were probably maintained by Native American burning. Fire compartment sizes in the Basin are relatively large and fires once started could have burned sizable portions of land. The combination of these factors, combined with the abundance of bison that congregated around the hundreds of natural salt licks, probably kept the Basin in a much more open state.
Recently, Edwin Bridges, a phenomenal botanist with experience throughout the Southeast and formally employed by the Tennessee Natural Heritage Program in the 1980s, shared a portion of a manuscript that he wrote in the late 1980s. Bridges co-described Pyne's Groundplum as a new species and in his original manuscript he had a section in the paper that he intended to be a part of his publication, but that reviewers suggested he remove. The section included a discussion of why he thought the Nashville Basin was much more open historically. It is unfortunate that this element of his paper was excluded from his final publication because it could have helped create a paradigm shift nearly 30 years ago, instead of that shift happening just within the past five years.
So, aside from the land survey data and anecdotal observations (experimental in the case of Pyne's Groundplum), what other evidence do we have in support of there historically being extensive savannas in the Nashville Basin?
Ordinarily, we would ideally go back and search for descriptions by early naturalists. The earliest references I've been able to find and that are reported in the primary papers on cedar glade ecology (e.g. the Baskins, Quarterman papers) date to just after the Civil War. Unlike some areas of the South (e.g. Georgia and the Carolinas), where there are excellent descriptions of the landscape and vegetation from times of early settlement, there are apparently no such descriptions from the Nashville Basin prior to the Civil War other than very vague references to salt licks near Nashville.
James M. Safford, the State Geologist for Tennessee after the Civil War, published extensively on the geology and physiography of the state during that period. He mentioned glades and noted that they were surrounded by forests of large redcedars. It is my opinion that this report was taken by later researchers, such as Quarterman and the Baskins, and used to justify that the matrix vegetation around glades should be dense forests with a high abundance of redcedar--a paradigm which endured throughout the 20th century even up until about five years ago, but one that contrasts sharply with evolving concepts that the glades were embedded in savannas, not dense forests. These forests and woodlands, which may be artificial in part, are recognized as a globally rare community by NatureServe, the Redcedar-Blue Ash Limestone Woodland.
One thing to keep in mind is that the Nashville Basin was settled in the 1780s-90s, some 70-80 years before Safford's description. This is plenty of time to allow for growth of large cedar trees in response to fire suppression that commenced right after settlement, which has been documented elsewhere across the South soon after settlement.
So, I contend that the conservation paradigm that we've held close to for so long now, that of not using fire in the glades, was based off descriptions of an already artificial landscape, greatly altered from its original state. How much harm has been done to the species of plants and animals (Northern Bobwhite, Eastern Meadowlark) that need more open conditions as a result of this paradigm?
If we look around the Nashville Basin, we can still see signs of the former savannas. Buried among the dense cedar thickets one can often find gnarled post oaks, chinkapin oaks, or even rarely blackjack oaks, that have heavy side branches, contorted trunks, and wide branches. It is entirely possible that many of these trees date to the period of first settlement. A dendroecological study is needed to be sure. There is no shortage of these old-growth trees throughout the Basin and many can be seen within the eastern city limits of Murfreesboro. Post oaks are most common in the rockier ground or areas with hydroxeric soils due to presence of a fragipan, which combined tend to occur in what is known as the Inner Nashville Basin (the heart of the glade ecosystem). In the deeper and richer-soiled Outer Nashville Basin, one tends to see large Chinkapin Oaks and an absence of Post Oak. In and north of Nashville in mesic areas along creeks or in pastures large Bur Oaks are sometimes seen. These three species are all known to be associated with savanna habitats in other parts of the eastern and midwestern US.
Another clue can be found along a few streams and rivers in the Basin. In southern Rutherford County along Dry Fork Creek and West Fork Stones River, the streambanks are lined in many areas with stands of Eastern Gamagrass (Tripsacum dactyloides). This species is most often associated with moist grasslands. This provides a clue that Gamagrass might have at one time been an important grass in deeper-soiled natural grasslands, meadows, and mesic savannas prior to the widespread introduction of European cool-season grasses such as fescue and bluegrass.
And perhaps the best clue of all is that there are still a couple of remnants of dry, rocky, savanna in the Inner Basin, but this grassland type no doubt remains as one of the rarest and most imperiled natural grasslands in the Southeast. Perhaps the best example can be seen east and southeast of the city of Murfreesboro. Along Factory Road, which incidentally is not far from one of the original localities where Edwin Bridges reported Pyne's Groundplum, is a remnant savanna of several acres. This savanna is located on private property directly adjacent to the road and across from Flatrock Glades and Barrens State Natural Area.
Top row: Limestone savanna along Factory Rd, Rutherford Co., TN with scattered post oaks. Note with fire the redcedar would not be nearly as abundant. Lower left: Baptisia aberrans (Blue Wild Indigo) is indicative of savanna. Bottom row, second from left: savanna at Gladeview Barren, Rutherford Co., TN. Second from right, bottom: Muhlenbergia capillaris grows in restored savanna at Flatrock Glades and Barrens State Natural Area. Bottom right: old-growth but small Chinkapin Oak, Couchville Glades and Barrens State Natural Area, Nashville, Davidson Co., TN. All photos by: Dwayne Estes.
This roadside probably looks to many like a typical rocky pasture to most, but a closer examination shows scattered post and chinkapin oaks, a lack of dense shrubs and redcedars, and a rich groundcover of grassland species that prefer deeper (but again still shallow and rocky) soil than those typical of open glades. Within this "field" are several small limestone glades that harbor typical glade endemics. This savanna remnant contains Glade Blue Wild Indigo (Baptisia aberrans), Gray-headed Coneflower (Ratibida pinnata), Cutleaf Prairie Dock (Silphium pinnatifidum), Wavy-Leaved Purple Coneflower (Echinacea simulata), and Naked-Stem Sunflower (Helianthus occidentalis). Across the road in the natural area are more species characteristic of limestone savanna, including Boykin's Milkwort (Polygala boykinii), Rough-leaved Rattlesnake Root (Nabalus asper), Prairie Gentian (Gentiana puberulenta), Cylindrical Blazingstar (Liatris cylindracea), and Prairie Dropseed (Sporobolus heterolepis). It seems that the most important native grasses in these xeric calcareous savannas is Little Bluestem (Schizachyrium scoparium) and Sideoats Grama (Bouteloua curtipendula). Prairie Dropseed was probably more frequent at one time.
The usual dominant grasses of Midwestern savannas, such as Indian Grass (Sorghastrum nutans) and Big Bluestem (Andropogon gerardii) are surprisingly rare in the Nashville Basin. Big bluestem is abundant southeast of Murfreesboro at what Dr. Hal R. DeSelm (Univ. of Tennessee) called the Gladeview Barren, named for the nearby Gladeview Church. At this site are other indicator species of savanna, as opposed to glades, including several of the species noted above, but also one of the few places in Tennessee for Purple Prairie Clover (Dalea gattingeri), Gattinger's Goldenrod (Solidago gattingeri), and White Four O'Clock (Mirabilis albida). The deeper-soiled rocky grasslands at Gladeview are dominated by Big Bluestem and Indian Grass.
The savannas of the Nashville Basin are truly rare and nearly extinct ecosystems. There were likely at least three or four types of savanna. Dry, rocky, areas with several inches of soil over bedrock supported xeric Post Oak Savanna. There are definite relicts of this community here and there throughout the Basin, though intact sites more than a fraction of an acre in size are nearly non-existent. The savannas of deeper, richer, moister soils are gone. They represent an extinct ecosystem and there are no intact remnants. A future blog will discuss how we are working to re-imagine this historical community and how we hope to rebuild it at sites in and around Nashville. The third type, wet calcareous savannas, likely developed over fragipan soils at a few select spots in the Inner Basin. With fire suppression these likely developed into close-canopied forested wetlands. Very small and fragmentary examples exist still of this essentially extinct community. Mostly they exist today as wet or seasonally wet meadows with an abundance of sedge and rush diversity, but their original composition has been greatly altered and we will never know what they were truly like.
One of the goals of the Southeastern Grasslands Initiative is to bring these lost ecosystems to light, to help coordinate and fund conservation efforts on the ground, to help fund the research needed to inform conservation, and to lead efforts to build essential seedbanks needed for conservation projects.
The staff of the Tennessee Division of Natural Areas have already shown it is possible to restore these savannas with their efforts at Flatrock State Natural Area. By using heavy machinery to remove thickets of recedar in combination with prescribed fire they have been able to restore savanna conditions. Several conservative species are recolonizing what were thickets.
We believe that we will be able to restore this forgotten part of the history of Middle Tennessee. It was this open landscape that Mississippian-era Native Americans called home up until the 1400s. It was the mutual hunting grounds of the Shawnee, Cherokee, Creek, Koasati, and Chickasaw tribes for centuries. It was in this open landscape that the bison roamed and carved traces that are today's highways and the abundant salt licks (like French's Lick which became downtown Nashville) that supported abundant game served as one of the main attractants for the earliest French and English explorers in the 1700s.
In rebuilding these lost ecosystems, we have the capacity to not only improve habitat for critically rare birds or birds once common but now in severe decline (e.g. Northern Bobwhite, Eastern Meadowlark) and rare plants, but we have the opportunity to tell an essential part of our early history, which presently cannot be shown to anyone because it really doesn't exist in an intact form.
There is no single place one can go now to learn more about these extinct savannas. There are no museum exhibits dedicated to them. There are no historical roadside markers that read "here was once extensive savanna." The remnants themselves and the sites that can be restored are fortunately still here and can serve as living museums and classrooms.
There is still hope...
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